I enjoy using x2go, but it's not exactly an easy to use system. If either end of the connection needs to change firewall settings or enter IP addresses, it's already far behind on usability. It could work with some setup in corporate environments, but doing this right is quite a pain for smaller businesses.

I agree that STUN/TURN servers are a necessity, but they're not _that_ expensive to self-host. You could stuff the STUN/TURN feature behind rate limits for the hosted version or put them behind a pay wall entirely so companies don't have to mess around with that stuff themselves.